[sdiy] TriggerIdiot

[Rick Jansen]

Well, I hope the sale of Atmel does not mean much for Arduino..

Here is my second Arduino-based machine: Trigger Idiot: A clock divider based gate trigger 
generator. Four rows with five rotary switches to set four clock pulse number per row that 
generate a gate signal per row. Knobs! LEDs! Switches! Buses!

<http://dropmix.xs4all.nl/rick/Emusic/TriggerIdiot/>

It is inspired by the Tiptop Audio Trigger Riot : 
<https://www.youtube.com/watch?v=AjKLewx17iQ>, but far simpler.

Current status is a finished front panel, but with the electronics still breadboard, and 
the software being work in progress.

I have no idea if this is an "obligatory" and totally obvious device. I had fun designing 
and building it, though.

Basically this is a device containing "midi" timing, internal/external/midi clock sources, 
and 20 rotary switches that can be read individually with an Arduino Uno, and a handful of 
I2C I/O expander PCF8574 chips.

A version with rotary encoders is in the pipeline. I like 12-position rotary switches a 
lot though, because you can read their setting as is, the settings are solid, are kept at 
power-down, etc. But, the range is just 12 steps. Rotary encoders are a bit more fuzzy to 
use, the (cheap) encoders I used are pretty noisy, so not easy to use to set a very 
precise value in one go. That 120 BPM setting with a rotary encoder suffers from overshoot 
and undershoot, though it is not too bad here. (I'll experiment more with applying C's for 
hardware debouncing, later.)

(This version used an Arduino Uno + I2C I/O expanders, the rotary encoder version will use 
an Arduino Mega only. It has enough I/O pins to not need I/O expansion. Actually, the 
PCF8574 chips are not expensive, but an Arduino Uno + 7 8574 costs a bit more than an 
Arduino Mega. Those Aduinos are lovely, and cheap!)


There were a few surprises too, building this:

1. My eyesight has gone!

I always enjoyed terriffic eyesight, both near and far, and was used to reading without 
glasses, and could read computer screens, cameras, iPhones etc even with glasses, although 
being a bit short sighted, until a few years ago.
No longer.
Yes, I must admit I have reached the Varifocus age too, fellow synth builders. And worse: 
soldering and miniature fiddling on a breadboard: TROUBLE! Even with regular reading glasses.

I was contemplating getting one of those big magnifying glasses some people use for 
knitting and needlework. But, I realized that strong reading glasses have a magnifying 
effect too. So I went to the HEMA (general store here) and bought myself a pair of strong 
reading glasse, strength +3. THAT WORKS FINE! Mind, it gives you a focus depth of not more 
than 20-30 cm, where things are sharp. The rest of the world is pretty blurry. So if you 
need that pair of pliers that is at the other end of your desk you need another pair of 
glasses. But for finnicky handiwork like this, a pair of +3 glasses is a relief! Glad I 
thought of that.

I am reminded of my old chemistry teacher, who was my age back then, and whom I pitied for 
having three pairs of glasses on his desk. So here I am. Pity me!
(damn!)


2a. The front panel

is a standard piece of 3 mm anodized aluminium for 19" rack, bought at Conrad. I no longer 
have an aluminium center nearby, so I thought to just order this. It's fine! A nice solid, 
thick piece of front panel. But, those standard 3.5 mm bus connectors have too short a 
thread to be fitted in a panel like this. It's simply too thick! Or the buses too short, 
whatever. I could just put the nut on the connector, but only just. What happens then is 
that if you stick a plug into the connector, you cannot insert it deep enough, and no 
proper connection is made. So I had to remove the nuts. The connector is now in place with 
just 2-component glue. (sorry)


2b. The front panel - MIRRORED PRINTING!

I did a design for the front panel, with spots where I needed to punch a dent for drilling 
holes. Rotary switches and rotary encoders have a second pin to make sure they are secured 
to a front panel. That need a second hole, but not a through hole. I happily was punching 
away until I realized that the second hole only needs to be present at the backside. And I 
was punching dents in the front. Sorry. Next time I'll PRINT THE FRONT PANEL MIRRORED. It 
will also prevent scratches like the one I made when the drill decided to not stay where I 
wanted it to be. Well, that is what prototypes are for.


3. Gate length

There is a rotary for BPM (0-255), and a second rotary for gate length (0-100). I was 
thinking along the lines of gate lengths that are 25-50% of the note length. However, with 
a rhythm-type device like this the gate lengths are pretty short. Just a few pulses of the 
midi clock.  Hm. Well, maybe it'll come in handy later for something else.

Anyway: <http://dropmix.xs4all.nl/rick/Emusic/TriggerIdiot/>

rick